There are a number of conditions or procedures which require repeated access to a blood vessel, an important example being hemodialysis.
There are three primary modes of access to the blood in hemodialysis: an intravenous catheter, an arteriovenous (AV) fistula, or a synthetic graft. The type of access is influenced by factors such as the expected time-course of a patient's renal failure and the condition of his or her vasculature. Patients may have multiple accesses, usually because an AV fistula or graft is maturing, and a catheter is still being used.
AV fistulas are recognized as the preferred access method, and are typically situated in the patient's arm (hand, forearm or elbow), but can also be situated in e.g. the patient's leg. To create such a fistula, an artery and a vein are joined together. Since this bypasses the capillaries, blood flows at a high rate through the fistula. This is required since the volumes of blood being withdrawn from, and therefore reintroduced to, the patient are high (typically 150-400 ml/min). Blood from veins is inadequate to meet these flow requirements, and repeated puncture of a large artery is not feasible. Further, a typical vein may not be suitable to handle such high volumes direct from a dialysis machine. Thus, by dividing a vein and connecting it to an artery via an AV fistula, the increased pressure of the blood (due to the blood bypassing the capillary beds) directly entering the vein from the artery enlarges the vein over time and thus allows for higher volumes of blood to be introduced to the vein. A fistula will take a number of weeks to mature, on average perhaps 4-6 weeks.
Access to an AV fistula may commonly be performed via a needle or a cannula, which requires puncturing the wall of the fistula. During a typical treatment, two needles may be inserted into the fistula, one to draw blood and one to return it. Repeated puncturing of the fistula can eventually lead to failure of the fistula via e.g. aneurysm or stenosis, which thereafter may require further surgery to create a new one or to unblock the existing one.
There is a need for a device which aids access to the vasculature, and which can help prevent excessive damage to a blood vessel or fistula occasioned by repeated access.